17

CHAPTERII

COPPER(II), NICKEL(II), COBALT(II) AND CHROMIUM(III)

COMPLEXES OF 1,4,8,11 CYCLOHEXADECANE AND 1,4,8,11

CYCLOHEPTADECANE

INTRODUCTION:

A large number of tetraazamacrocycles (both saturated and unsaturated)

have been prepared during the last fifteen years and their metal complexes studied.

Most of the work in this area involves the 14membered macrocycles(12,117,118)

which form the most stable complexes. These results show that in the case of

1,4,8,11 tetraazacyclotetradecane (L1) which carries a 5,6,5,6 membered chelate

ring sequence, the cavity is a best fit case for cobalt(III) and to a very large extent

for nickel(II) as well. This conclusion is based on detailed investigations on the

spectral(119,120), magnetic(121), thermodynamic(35,88,122,123), kinetic(79,82,98100) and

electrochemical aspects(124) of the 12 to 16membered tetraaza macrocycles.

In may be noted that the most important factor which determines the extent

of coordination of the transition metal ions with the macrocyclic ligands

containing nitrogen, oxygen and/or sulphur donor atoms is the relative matching of

the cavity size with the dimensions of the metal ion(125,126). In the case of nitrogen

donors (with fully saturated macrocycles) a further factor, the ligand’s ability to

satisfy the electronic and geometric preferences of the coordinated metal, is also

operative(127). It is thus observed that for two isomeric 14membered macrocycles,

1,4,8,11 tetraaza tetradecane(L1) (aso referred to as cyclam) and 1,5,8,11 tetraaza

cyclotetradecane (L2) (also referred to as isocylam), the former(L1) satisfies the

above conditions to give more stable complexes as compared to the latter (L2)(123).

The 6,5,5,6 chelates sequence in isocyclam(L2) is thus unfavourable as compared

18

to the 5,6,5,6 sequence in cyclam(L1), although the two ligands are expected to

have similar cavity sizes(123). Similar conclusions have been drawn by comparison

with the complexes of L3 which shows that the geometrical constraints imposed by

the insertion of a pyridine ring(128) prevent the ligand from fully satisfying the

geometrical requirements of the central metal ion.(129)

HNNH

HNNH

6

6

5 5

NHNH

HNNH

6

5

5

6

NHNH

HNNH Me

6

5

5

6

L1 L

2 L3

The above inference are in accord with the kinetic stability of these

complexes, where it has been observed that [Ni L1]2+ persists in acid solutions for

months[8], while in the case of macrocycles carrying bigger chelate rings, as in L4,

this stability is markedly decreased (99). Substitution of the imine nitrogens of

cyclam with nitrile groups (L5) also has a labilizing effect on the kinetic stability

of the complex towards acids(98). A recent investigation(35) on a new

14membered tetraaza macrocycle, 1,4,7,10 tetraazacyclotetradecane (L6) shows

that the seven memebred chelate ring (not encountered very often) in the 5,5,5,7

chelate sequence has a destabilizing effect due to the unfavourable entropy

contribution of this ring(130,131). In order to investigate the effect of such larger

chelate rings on the stability of the macrocyclic complexes, two new 16 and

17membered macrocycles(1,4,8,11 tetraazacyclohexadecane(L7) and 1,4,8,11

tetraazacycloheptadecane (L8) have been prepared and their copper(II), nickel(II),

cobalt(III) and chromium(III) complexes investigated, which give a 5,6,5,8 and

5,6,5,9 sequence of chelate rings.

19

HNNH

HNNHNCH2CH2C

NCH2CH2C CH2CH2CN

CH2CH2CN6

6

5 5

L5L

4

NNH

CH3 CH3

NHN

CH3 CH3

NHNH

HNNH

L6

20

EXPERIMENTAL

The ligands were prepared essentially using the method described by Smith

et.al(32). The tetratosylated linear tetraamine was condensed with the bistosylated

diol (1,5 pentane diol or 1,6 hexane diol) in DMF(132) to give the cyclised product,

which was hydrolysed in conc. H2SO4 to give the free macrocycle. The details of

the method are as described.

Preparation of 1,4,8,11 tetraazaundecane (2,3,2 tet)

2,3,2 tet (L9) was prepared from ethylenediamine and 1,3 dibromopropane

by a method similar to the one described for 3,2,3 tet(133).

12 mol (720 g) of 1,2 diaminoethane was placed in a 3L three necked flask

fitted with a mechanical stirrer, a thermometer and addition funnel. 1,2

diaminoethane was cooled to 0C and to this 1 mol (202g) of 1,3 dibromopropane

was added dropwise stirring maintaining the temperature at 0C during the

addition, which took about 2h. The mixture was then heated for about 1h on a

steam bath and concentrated to about onethird its volume on a rotary evaporator

by distilling off the excess 1,2 diaminoethane. The concentrated mixture was then

treated with 150g of potassium hydroxide flakes slowly and heated on a steam

bath for a further 2h with efficient mechanical stirring. After cooling to about 5C

in ice, the solid potassium bromide was filtered off carefully and the solid washed

with several portions of ether. The filtrate and washings were combined and the

ether flashed off on a rotary evaporator. Any solids that appeared were again

filtered off and the procedure repeated till the filtrate was completely free of any

solid and was in the form of a colourless, transparent oily liquid. The viscous oil

was vacuumdistilled using a 1020 cm vigreux column and the fraction distilling

21

over between 135140C at 3 torr was collected to give the pure 2,3,2 tet which

was stored in a dark colored brittle in a refrigerator.

The tetramine was protected from moisture by sealing the bottle with wax as

the amine forms a solid hydrate with moist air. The condensation reaction may be

represented as

2NH2 (CH2)2NH2 + Br(CH2)3Br

+ + NH2(CH2)2NH2(CH2)3NH2(CH2)2NH2 + 2Br

2KOH

NH2(CH2)2NH(CH2)3NH(CH2)2NH2 + 2KBr + 2H2O

The purity of the sample was checked through gas chromatography.

Preparation of N,N|,N||, N|||tetrakis (ptoluenesulphonyl) 1,4,8,11

tetraazaundecane

N,N|,N||, N|||tetrakis (ptoluenesulphonyl) 1,4,8,11 tetraazaundecane was

prepared by a similar method to the one described by Hay(134).

0.25 ml (40 g) of 2,3,2 tet was placed in a 2L beaker fitted with

mechanical stirrer and mixed with 1.1 mol (44g) of NaOH dissolved in 200 cm3 of

water. To this 1.0 mol (190.5g) of ptoluenesulphonylchloride dissolved in 1L of

ether was added dropwise with constant stirring over a period of about 4h. After

complete addition, the mixture was stirred for 1h and 2L of water added with

stirring. The mixture was allowed to stand overnight and the gummy mass

removed by decantation. The brown gummy product was washed several times

with water and dissolved in 200 cm3 of chloroform. The chloroform layer was

filtered and dried with anhydrous calcium sulphate. The dried chloroform solution

was then placed in a rotary evaporator and chloroform stripped off leaving behind

a gummy mass which on standing for a few days gave a brown glassy solid.

22

Preparation of 0,0|bis (ptoluenesulphonyl) 1,5 pentanediol and 0,0|bis

(ptoluenesulphonyl) 1,6 hexanediol

This compound was also prepared by a method similar to that described(135).

0.2 mol (20.8g) of 1,5 pentanediol (or 23.6g of 1,6 hexanediol) was placed

in a four necked flask equipped with a mechanical stirrer, thermometer and

nitrogen inlet tube. To this 100 cm3 of dry pyridine (distilled over KOH) was

added and to the fourth neck an addition funnel was attached containing 0.4 mol

(76.5 g) of ptoluenesulphonylchloride dissolved in 100 cm3 of dry pyridine. The

reaction mixture was cooled to 0C in an icesalt bath and ptoluenesulphonyl

chloride solution added at such a rate (with vigorous stirring and under a stream of

nitrogen) so as to maintain the temperature below 5C. After complete addition,

the mixture was stirred for 2 to 3h under nitrogen, keeping the temperature below

5C. After this period, 150 cm3 of of conc.HCl diluted to 600 cm3 and cooled in

ice was added dropwise with stirring and maintaining a low temperature. After the

addition was complete, a further 400 cm3 of water was added and the white

product filtered off, washed with cold water, some 50% ethanol and dried in a

vacuum over at 5060C.

Cyclisation step

0.1 mol of N,N|,N||,N|||tetrakis (ptoluenesulphonyl) 1,4,8,11 tetraazaun

decane was dissolved in 1L of anhydrous DMF (dried over molecular sieves for

48h and distilled over CaH2 under vacuum) and oxygen free nitrogen bubbled to

deaerate the solution. This was then placed in a 3L three necked flask carrying a

mechanical stirrer. To this 0.22 mol of NaH (suspended in oil) was added in small

portions over a period of 2 to 3h. The solution was further stirred for 4h. Nitrogen

was bubbled all throughout and also during the subsequent steps. After this period,

23

the solution was heated to 110C on an oil bath and 0.1 mol of the tosylated diol

dissolved in 200 cm3 of dry DMF was added over a period of 2 to 3h. The solution

was then further heated at 110C for 4h, concentrated to about 200 cm3 on a rotary

evaporator and the concentrate dropped slowly into 1.5L of cold water. The

precipitate was filtered off after standing overnight. The crude product was

dissolved in 200 cm3 of hot chloroform and mixed with 1.5L of ethanol and

allowed to stand overnight. The white recrystallised product was filtered off,

washed with ethanol and dried in a vacuum oven at 60C. The purity of the

cyclised product was checked through infrared spectra. The pure cyclised product

does not show any NH band around 3200 cm1.

Hydrolysis of the tetratosylated macrocycle and extraction of the free

macrocycle

The tetratosylated macrocycle obtained above was dissolved in 150 cm3 of

conc. H2SO4 and heated at 100110C on an oil bath with constant magnetic

stirring for 3 days. The dark brown solution was cooled to 0C in an icesalt bath

and treated carefully with 1L of icecold absolute ethanol followed by 1L of

ether and the mixture allowed to stand for a few hours. The brownish precipitate

was filtered off., washed with some ethanol and ether. It was then suspended in

water (ca. 200 cm3) and treated with a saturated solution of NaOH, sufficient to

raise the pH to above 13. The resulting solution was extracted with 810 portions

of 200 cm3 of chloroform. After 45 extractions, anhydrous Na2SO4 (ca.100g) was

added to salt out the free macrocycle. The chloroform extracts were dried with

anhydrous sodium sulphate and the chloroform stripped off on a rotary evaporator

to give an oily liquid, which on cooling gave a yellowish sticky solid. Mass spectra

showed m/e = 228.37 for 1,4,8,11 tetraazacyclohexadecane (calc. m/e = 228.384

24

for C12H28N4) and m/e = 242.41 for 1,4,8,11 tetrazacycloheptadecane (calc. m/e =

242.411 for C13H30N4).

Preparation of L.4HCl

1g of the liquid was dissolved in 5 cm3 of methanol and cooled in ice. To

this 10 cm3 of ice cold conc.HCl was added dropwise with stirring and cooling in

ice followed by 50 cm3 of ethanol. The white product was filtered off, washed with

ethanol/ether and dried in vacuum.

Preparation of Complexes

1. Na3[Co(CO3)3]

Sodium tris(carbonato)cobalt(III) was prepared by the method described

by Bauer(136).

29.1g of Co(NO3)2.6H2O in 50 cm3 of water mixed with 10 cm3 of 30%

hydrogen peroxide (excess) was added dropwise with stirring to a cold slurry of

42.0g of sodium bicarbonate (0.50 mole) in 50 cm3 of water. The mixture was

allowed to stand at 0C for 1h with continuous stirring. The olive green product

was filtered off, washed three times with 10.0 cm3 portion of cold water, then

washed with absolute alcohol, dry ether and dried in vacuum.

2. [CuL](ClO4)2

0.02 mol. of the ligand and 0.02 mol of Cu(ClO4)2.6H2O were dissolved in

25 cm3 of methanol and heated on a steam bath for 1 h to give a deep blue colored

solution. The volume was reduced to about 3 cm3 and ether added to precipitate

the complex, which was filtered off. The crude product was purified by dissolving

in a minimum quantity of hot methanol, cooling and precipitating with ther. The

product was filtered off, washed with isopropanol, then ether and finally dried in

vacuum.

25

3. [NiL)(ClO4)2

0.02 mol of the ligand and 0.02 mol of Ni(ClO4)2.6H2O were dissolved in

25cm3 of methanol and heated on a steam bath for 2h. The yellow solution was

filtered hot and the volume of the filtrate reduced to about 3 cm3. Ether was added

to precipitate the complex. The crude product was purified by dissolving in a

minimum quantity of methanol and precipitated with ether. The purified, shining

yellow product was filtered off, washed with isopropanol, then ether and dried in

vacuum.

4. Trans(CoLCl2](ClO4)

MethodA

0.8 g of freshly prepared sodium tris(cabonato)cobalt(III) and 0.8 g of

L4HCl were mixed in 30 cm3 of 1:1 (V/V) methanolwater mixture and heated

on a steam bath slowly till the effervescence ceased (ca. 10 min) and then heated

for another 30 min. To the deep red slurry, 5 cm3 of conc.HCl was added and the

green solution heated on a steam bath till the volume was reduced to about 3 cm3.

The solution was cooled in an ice bath and treated with 1 cm3 of 70% HClO4. The

green product was filtered off, washed with ethanol and then ether. It was finally

dried in vacuum.

MethodB

0.04 ml of the ligand and 0.04 mol of Co(CH3COO)24H2O were dissolved in

30 cm3 of 1:1 methanolwater mixture and the solution aerated for about 5h to

give a deep red solution. To this 5 cm3 of cold conc.HCl was added and the

volume reduced to half by bubbling air. To the cold green solution, 1 cm3 of 70%

HClO4 was added carefully. No precipitate appeared at this stage. The volume was

reduced on a steam bath to about 5 cm3 and the mixture cooled in ice. The green

26

product was filtered off, washed with ethanol then ether and finally dried in

vacuum. Further concentration of the motherliquor gave a small amount of green

product, which on recrystallisation from methanol was found to give an infrared

spectra identical to the first crop.

5. Trans[CoL(NO2)2]ClO4

0.01 mol of trans[CoLCl2]ClO4 was dissolved in 20 cm3 of hot methanol

and treated with 0.14g of sodium nitrite. The mixture was slowly heated on a

steam bath till the solution turned brownish yellow (ca. 20 min) and filtered hot.

The volume of the filtrate was carefully reduced to half on a steam bath and

cooled. The brownish yellow product which crystallizes out was filtered off,

washed with ethanol, then ether and dried in vacuum.

6. Trans[CoL(NO2)Cl]ClO4

0.01 mol of trans[CoL(NO2)2]ClO4 was warmed for about 10 min at 60C

in 10 cm3 of dil. HCl during which time the initially yellow solution turns pinkish.

The solution was cooled and treated with 2 cm3 of 70% HClO4 which results in an

immediate precipitation of the pink complex. The product was filtered off, washed

with ethanol till free from acid and dried in vacuum.

7. Cis[CoL(acac)](ClO4)2

0.01 mol of trans[CoLCl2]ClO4 was suspended in 5 cm3 of methanol and

treated with 0.2g of acetyl acetone. The mixture was heated on a steam bath for

ca.5 min and 10 drops of diethylamine added when a deep red solution was

obtained. Heating was continued for another 10 min after which 0.5g of

LiClO4.H2O was added. Cooling in ice gave a deep red colored product, which

was filtered off, washed with isopropanol, ether and finally dried in vacuum.

27

8. Cis[CoL(glycine)](ClO4)2

0.01 mol of trans[CoLCl2]ClO4 was suspended in 5 cm3 of 1:1 methanol

water mixture (V/V) and mixed with 0.1g of glycine. 10 drops of diethylamine

were added to the mixture after heating it to about 70C on a steam bath and the

resulting deep red solution heated further for a few minutes. To this 0.2g of

LiClO4.H2O were added, the solution cooled and the complex precipitated as an oil

by the addition of excess ethanol. The red oily product on tituration several times

with ethanol gave a red solid, which was filtered off, washed with ethanol, ether

and dried in vacuum.

9. Cis[Co[16]ane N4) (nethanolamine)Cl](ClO4)2

This compound was prepared by the general route described by Hay(137).

0.01 mol of trans[Co([16]ane N4)Cl2]ClO4 was moistened with a few drops of

water, mixed with a slight excess (0.015 mol) of nethanolamine and ground to a

fine paste. The color changed rapidly from green to red, characteristic of the

CoN5Cl chromophore. To the fine paste a small amount of ethanol (ca. 10 cm3)

was added and the mixture stirred well. The red oily product was separated by

decantation. The oily residue on tituration with ethanol gave a red solid, which

was filtered off, washed with ethanol and ether. The red product was highly

hygroscopic and gave a stickly solid on standing and hence could not be subjected

to satisfactory analysis.

10. Chromium(III) Complexes

The chromium(III) complexes were prepared by the following general

method.

0.004 mol (1.10 g) of chromium(III) chloride hexahydrate was dissolved in

150 cm3 of dry DMF and the solution distilled until the distillate boiled over

28

between 152153C and the volume of the solution reduced to about 10 cm3. At

this stage, the distillation was interrupted and 4.09 mmol of the ligand added to the

hot solution. The mixture was heated for about 10 min and then cooled. The

precipitated product was filtered off and washed with dry DMF, then ether and

dried in vacuum. The product was dissolved in minimum hot methanol, filtered

and concentrated to a small volume on a rotary evaporator. On standing, a pink

coloured product deposits, which was filtered, washed with DMF, ether and dried

in vacuum. The products were found to be cis[CrLCl2]Cl for both the ligands.

The trans[CrLCl2]Cl complex was prepared for the [16] ane N4 ligand

through an alternate route as follows:

0.004 mole (1.10g) of chromium(III) chloride hexahydrate was dissolved in

5 cm3 of dry DMF and treated with 15 cm3 of 2,2| dimethoxypropane. The solution

was heated at about 120C, till it turned pink when 0.004 mol (0.90 g) of [16] ane

N4 was added to the hot solution. Heating was continued for another 510 min,

after which the solution was cooled and the product filtered off, washed with dry

DMF, ether and finally dried in vacuum. The crude product was dissolved in a

minimum hot methanol, filtered hot and concentrated to yield a greenish product

on cooling. This was filtered off and washed with ether. The product was

suspended in hot isopropanol and stirred for a few minutes and filtered. The pure

light green product was washed with isopropanol, ether and dried in vacuum.

The chloride complexes were converted to the perchlorate form by

dissolving [CrLCl2]Cl in a minimum quantity of water and adding some saturated

NaClO4 solution. The complex [CrLCl2]ClO4 separates out immediately. The

product was filtered off, washed with cold water, ethanol, ether and dried in

vacuum.

29

The analytical data of the complexes is presented in Tables 1 and 2.

Kinetic Measurements:

The acid catalysed dissociation of the copper(II) complexes was studied

using perchloric acid solutions adjusted to I = 1.0M with NaClO4. The kinetic runs

were carried out with a solution of 0.05 g of the copper(II) complexes dissolved in

50 cm3 of 1.0M NaClO4. Since the dissociation proceeds at a very rapid rate, the

kinetic runs were monitored using stopped flow techniques. The reactions were

monitored at 37735 cm1 for [Cu([16]ane N4)(ClO4)2 and at 38461 cm1 for

[Cu([17]ane N4)](ClO4)2. The reactions were studied with DubrremGibson

stopped flow system. The data was stored in a transient recorder and displayed on

an oscilloscope screen. The useful kinetic data was transferred from the transient

recorder to an interfaced desk top computer (commodore with 16K memory) for

calculation of the rates (kobs). At least six concordant runs with a correlation

coefficient of >.999 (for first order dependence in complex concentration) were

used to evaluate the rates at each acid concentration. The rates were averaged over

at least three halflives in each case.

The routine and interval scan spectra were recorded on a Perkin Elmer 402

spectrophotometer.

Polarographic Studies:

Polarographic studies were carried out on a Cambridge pen recording

polarograph using a dropping mercury electrode. The polarograms of 0.001 M

solution of the copper(II) complexes were recorded in aqueous media using a

conventional saturated calomel electrode as a reference electrode in 0.1M KCl

and/or 0.1M NaClO4 solution as supporting electrolyte. 0.02% solution of triton

X100 was used as maxima suppressor. Before recording the polarograms the

30

solutions were deaerated by bubbling purified nitrogen through the solutions for

about 15 min.

Physical Measurements:

Chemical analysis and mass spectra of the samples were carried out at the

C.D.R.I., Lucknow. The infrared spectra were determined in KBr discs using

Beckman IR20 spectrophotometer. Conductivity measurements of 103 mol cm3

aqueous solutions of the complexes were made at 25 0.1C on a systronics

conductivity bridge type 302.

RESULTS AND DISCUSSION:

The results of these studies show that the ligands, 1,4,8,11

tetraazacyclohexadecane and 1,4,8,11 tetraazacycloheptadecane, can be readily

obtained through the cyclisation of the tosylated segements (tetratosyl of 1,4,8,11

tetraazaundecane and bistosyl of 1,5 pentanediol or 1,6 hexanediol) with a yield of

about 40% [ca. 10g starting from 16g (0.1 mol) of 1,4,8,11 tetraazaundecane].

Both the ligands undergo complexation quite easily with copper(II), nickel(II),

cobalt(III) and chromium(III). The cobalt(III) complexes are quite stable and

undergo axial ligand substitution reactions by the usual metathesis procedures.

This is despite the presence of bulky cyclic segments which give 8 or

9membered chelate rings. The facile complexation is apparently promoted by

virtue of the 2,3,2 tet sequence which holds the four nitrogens in a synthetically

preoriented geometry favourable for coordination. It may be noted that cyclam

(L1) which forms the most stable complexes has also got a similar 2,3,2 tet

sequence, the only difference being in the size of the fourth chelate ring. The

successful isolation of these complexes is unique in the sense that both 8 and

9membered chelates are rarely encountered. Normally the bigger rings are

31

associated with very low stability which has been ascribed by

Schwarzenbach(130,131) to an unfavourable entropy contribution. The stabilization of

these large rings can be ascribed to the alternating sequence of five and six

membered chelate rings which is enthalpically preferred(35). The sequence is

preferred since in such an arrangement, the ligand is able to dispose its donor

atoms closest to the sites preferred by the metal ion, at the corners of the equatorial

square in tetragonally distorted octahedral complexes.

Copper(II) Complexes:

The copper(II) complexes are bluish violet and show a single dd band

(Table 3). This compares quite well with other copper(II) tetraaza macrocyclic

complexes. It is intringuing to note the close similarities in the extinction

coefficient values of the complexes carrying the 5,6,5 chelate sequence. The

infrared spectra shows a sharp NH band around 3220 cm1 and the perchlorate

bands at 1100 and 620 cm1 (Table 4 and 5). Since there is no splitting in the

asym (ClO) band at 1100 cm1, the perchlorate is present in an ionic state in the

solid complex. Conductometric measurements in aqueous solution show that these

two complexes are 2:1 electrolytes (Ω171 S cm2 mol1 for [Cu([16]ane

N4)](ClO4)2 and (Ω150 S cm2 mol1 for [Co([17]ane N4)](ClO4)2 at 25C).

Nickel(II) Complexes:

The nickel(II) complexes are yellow in colour and show a broad band at

22222 cm1 for [Ni([16]ane N4)](ClO4)2 and 21733 cm1 for [Ni([17]ane N4)]

(ClO4)2 due to combination of the 3A2g 3T1g(p) transition of octahedral nickel(II)

and 1A1g 1B1g transition of square planar nickel(II). The extinction coefficient

values for these two complexes are quite low and show temperature dependence.

This observation suggests an octahedral square planar equilibrium.

32

Kodama and Kimura(138) have recently observed an octahedral planar

equilibrium in the nickel(II) complex of 1,4,7,10 tetraazacyclododecane3,12

dione. Such octahedral planar equilibrium are well established for a

variety of nickel(II) complexes(26,140). The equilibrium shifts towards the planar

form with increase in temperature or addition of inorganic salts like NaClO4(139,141).

This behaviour(142) is consistent with the equilibrium [NiL(H2O)2]2+ [NiL]2+

+ 2H2O.

In the case of an analogues complex, cmeso5,12 dimethyl 1,4,8,11

tetraazacyclotetradecane, only a single dd band is observed at 21410 cm1 (=64

dm3 mol1 cm1)(155). For this complex, it has been evaluated that at 25C, there is

ca 65% of the octahedral species and 35% of the planar species. This equilibrium

is endothermic and shifts to right on an increase of temperature. An increase in the

concentration or inert salts like NaClO4, reduces the ‘free’ water concentration

which again shifts the equilibrium to the right. Such equilibria exhibit values of

H in the range of 7.1 to 6.2 kJ mol1 and S298 of the order of 20 to 140J mol1

over a temperature range of 2050C for a variety of complexes. The temperature

dependence of K gives the value of H and S298.

It has been suggested that the relatively low entropy for the equilibrium

involving [Ni([12]ane N4)]2+ arises due to the formation of a five coordinate

complex rather than a four coordinate complex, leading to the loss of a fewer

water molecules.(143)

The infrared spectra shows the NH band at 3200 cm1 and the ionic

perchlorate at 1100 and 620 cm1. Conductance measurements show these

complexes to be 2:1 electrolytes in aqueous solution (Ω 171 S cm2 mol1 for

33

1,4,8,11 tetraazacyclohexadecane and Ω 191 S cm2 mol1 for 1,4,8,11 tetraaza

cycloheptadecane 15 25C).

Cobalt(III) Complexes:

The macrocycles give green colored cobalt(III) complexes, trans

[CoLCl2]ClO4, which show a dd band typical of a CoN4Cl2 chromophore (Table

3 and 4). This band compares favourably with the reported dd band for other

cobalt(III) tetraaza macrocyclic complexes carrying the same chromophone. A

number of other trans[CoLX2]ClO4 and cis[CoLY](ClO4)2 complexes have been

prepared by ligand metathesis reactions. The visible spectra of these complexes are

typical of CoN6, CoN5Cl, CoN5O or CoN4O2 chromophores (Table 3 and 4). The

position of these bands supports the assignment of trans and cisconfiguration to

these complexes. These values are comparable with other reported literature values

for similar complexes.

Complexes with the trans[(CoN4X2)]n+ chromophore, with X=Cl, normally

show three low intensity bands in the visible region. Such complexes have a basic

D4h symmetry, with 1A1g 1T1g(Oh) transition split into two components.

1A1g 1Eg(D4h) and 1A1g 1A2g(D4h)(144,145), where the tetragonal splitting

is small (when X and N do not differ very much in their positions in the spectro

chemical series), only a single absorption band is observed under the 1A1g1T1g(Oh) envelope.

Formation of ciscomplexes require the ligand to have an Nracemic

configuration which provides a fold axis to enable the ligand to fold. Secondary

NH protons rapidly exchange in basic conditions (above pH6) and this process has

been studied kinetically with a number of nickel(II) complexes with ligands of this

type(146). The use of diethylamine allows conversion of Nmeso diasteroisomers to

34

the Nracemic diastereoisomer required for the formation of the ciscomplexes.

The ligand has a folded conformation in a ciscomplex with a C2 axis(147) as shown

in [A].

N

Co

N

X

X

N

N

H

H

C2

[A]

The isolation of ciscomplexes with acac and glycine show that the present

ligands readily fold in presence of diethylamine to give the cisgeometry. The

isomerisation of the Nchiral centres is base catalysed(148). The base catalysed

configurational conversion occurs while the ligand is coordinated and has been

explained on the basis of a concerted mechanism involving reaction of coordinated

hydroxide ion with the amine hydrogers(148,149).

The infrared spectra of these complexes (Table 4 and 5) show bands

corresponding to the macrocycle and the appropriate axial ligands. The NH band

appears at ca. 3200 cm1. Its position changes presumably due to hydrogen

bonding within the complex.

The skeletal vibrations of the macrocycles, in the 7501500 cm1 region,

reflect changes in the geometry of the macrocycle. A comparison of the spectra of

[CoL Y]n+ (Y = glycine or acac) with that of [CoLCl2]n+ reflects the differences

between the folded geometry in the former cases and the planar geometry in the

latter. Bands observed in the chlorocomplex are either shifted or not observed at

all in the ciscomplexes. The characteristic bands due to chelated acetyl acetonate

ligand appear around 1570 cm1 and 1520 cm1. The glycine complex shows a

35

broad band at 1340 cm1 assigned to the asymmetric stretching vibration of the

coordination COO group and another band at 1600 cm1 due to the symmetric

stretching of the COO group. The unidentate ligand NO2, which occurs in two

complexes, shows the characteristic bands due to asym(NO2), sym(NO2) and

(NO2) (Table 4 and 5).

Chromium(III) Complexes:

The results show that the chromium complexes can be readily prepared by

the reaction of trichloro tris(N,Ndimethylformamide) chromium(III) (produced

by the dehydration of CrCl3.6H2O in N,Ndimethylformamide) with the saturated

N4 macrocyclic ligands quite readily. It is interesting to note that the distilling

DMF route gave predominantly the cisisomer while the 2,2| dimethoxy propane

route gave predominantly the transisomer. The cis and transisomers can be

easily distinguished on the basis of their infrared (Table 4 and 5) and visible

spectra (Table 3).

The pink coloured cisisomer, cis[CrLCl2]Cl and cis[CrLCl2]ClO4, show

two NH bands appearing around 3150 cm1 and 3200 cm1. These observations

are similar to those for cis[CrMe2[14]ane Cl2]Cl (L1) and cis[Rh cyclam Cl2]+

(L14) where two NH bands are observed at 3160 and 3060 cm1[150] and 3175 and

3060 cm1 [151] respectively. In contrast the light green coloured trans complexes,

trans[Cr([16]ane N4) Cl2]Cl and trans [Cr([16]ane N4)Cl]ClO4, show a single

NH band around 3200 cm1.

The above assignment is confirmed by dd spectra as well. The more

symmetrical transisomer of [CrN4Cl2]+ complexes [N4 = system with four

nitrogen donors] normally have extinction coefficients of < 30 and the lowest dd

36

band appears in the 1750016900 cm1 range(152,153). The less symmetrical

cisisomers have much higher extinction coefficients (of the order of 80120) and

the lowest dd band occurs in the 1890017500 cm1 region. The present

complexes also show absorption bands in these regions in accord with their

assigned geometries.

The ease of formation of ciscomplexes with chromium(III) is in marked

contrast to the behaviour observed with cobalt(III) where the transcomplexes are

generally formed with the tetraaza ligands(154).

Stereochemical Considerations:

The macrocycles are capable of forming a novel sequence of chelate rings

(5,6,5,8 and 5,6,5,9) on undergoing complexation. The complexes of these ligands

carry four chiral nitrogen centres, which can yield as many as ten

Ndiastereoisomers (Scheme 1, this is representative for both the macrocycles)

similar to the ones possible for cyclam and Cmeso5,12 dimethyl 1,4,8,11

tetraazacyclotetradecane(155). Molecular models show that out of the possible ten

diastereoisomers, only four isomers(I,II,III,IV) are virtually free from torsional

strain as well as have minimum hydrogenhydrogen interactions in the chelate

rings.

In this form the six membered ring is in the chair form, while both the five

membered chelate rings are in gauche form(156). In the case of the bulky eight and

ninemembered chelate rings, both the imino hydrogens are in an Nrac

configuration.

The green trans[CoL Cl2]ClO4 complex has been prepared by two

synthetic routes: (a) reaction of the ligand hydrochloride with sodium

tris(carbonato) cobalt(III) and (b) aerial oxidation of cobalt(II) acetate solutions

37

38

containing the ligand. Both the routes gave single products which had an identical

infrared and visible spectra. It is known that the former route may involve a

ciscarbonato species as the intermediate and can give a mixture of the

Ndiastereoisomers(157158). The later route (involving aerial oxidation) gives the

pure diastereoisomers and under carefully controlled conditions, the

Ndiastereoisomers separate out at different stages of the preparative procedure by

virtue of their different solubilities. This method has been successfully used to

separate the various Ndiastereoisomers of the cobalt(III) complexes of Cmeso

and Crac5,12dimethyl 1,4,8,11 tetraazacyclotetradecane(159). These isomers

give different infrared and visible spectra. Since both the routes give the same

isomers, the ligand must be existing as a single diastereoisomer in its

thermodynamically most stable form.

In the case of cyclam (which is also characterized by a 5,6,5 chelate ring

sequence) it has been shown that the ligand exists in the form (B)(82,160,161), a

structure often referred to as the cyclam or transIII form(160).

N

N

N

N

HH

HH

[B]

It is thus expected that the present ligands should have a similar configuration (VI)

and can also be represented by the projection structures XI and XII.

39

Electronic Spectra:

The complexes of copper(II) generally show square planar or tetragonally

distorted octahedral structures, for which broad bands are observed due to the

overlap of a1gb1g, b2g b1g and b2g b1g transition in the visible region(162). The

b2gb1g transition is equal to the difference in the energies of the dxy and dx2y

2

states, i.e. equal to the inplane 10 Dq or 10 Dqxy. This is very close to the other

two transitions which are merged with it and hence the max of the broad band

gives an approximate value of 10Dqxy. Since, in the macrocyclic complexes of the

type [Cu Mac]2+ there are no axial ligands, the value of max corresponds to the

field created by the macrocycle in the square plane. It has been shown for

copper(II) polyamine complexes, having a tetragonal stereochemistry that this

empirical parameter corresponding to (dd) is proportional to the strength of the

metal nitrogen in plane interactions(163). It has been shown by Bhattacharya(120)

that the order of field strength in terms of ring size is

14 > 13 > 15 > 16

According to Bhattacharya(120), in the case of the bigger 15 and

16membered rings, the ligand experiences a strain in arranging its donor atoms at

the corners of a square plane around the copper(II) ion. The structure is probably

40

planar with lengthened CuN bonds. The weaker CuN interaction results in a

lower of Dqxy value. Further, with the smaller rings, the 14membered ring is a

best fit case while in the 13membered ring the cavity is smaller for the copper(II)

ion. Hence it sits ‘atop’ the N4 arrangement. Such a square pyramid arrangement

has been suggested by Lever(164,165) and results in weaker CuN interactions.

Similar suggestions for the square planar coordination in the case of 13membered

macrocyclic complexes have been suggested by Paoletti(129,165) also.

A comparison of the spectral data on a variety of Copper(II) complexes with

saturated cyclic tetramines (Table 6) shows that besides the cavity size, the

sequence of the occurrence of chelate rings and their size plays a dominant role in

deciding the strength of the coppernitrogen interaction. It may be noted that

cyclam, with a 5,6,5,6 chelate ring sequence, forms the most stable copper(II)

complex, since it is able to dispose its donor nitrogen atoms closest to the metal

ion preferred sites at the corners of the equatorial square in a tetragonal geometry.

The loss of CuN bond strength in the ligand L6 has been ascribed to the

introduction of the bulky seven membered chelate ring(35). In addition to the bulky

seven membered chelate ring, the 5,5,5 chelate ring sequence is also responsible

for lowering of the CuN interaction. This conclusion is supported by the results

of the present studies which show that inspite of the introduction of the bulky 8

and 9 membered chelate rings, the strength of CuN interaction is comparable to

that of the ligand L6. The 5,6,5 sequence of the chelate rings in L7 and L8 place the

nitrogen donors into a ‘Synthetically preoriented’ geometry favourable for

coordination.

The trends observed in the values of (dd) for these complexes are also

reflected in the H(aq) values(35). The enthalpy values for some of these

41

complexes show that the 5,6,5 chelate ring sequence enjoys an enthalpic advantage

over the other chelate ring sequence (Table 6). The large strain expected by

introduction of the 8 and 9membered chelate rings is compensated to a large

extent by the 5,6,5 chelate sequence.

The ultraviolet spectra of the Copper(II) complexes (Table 3) show a single

band corresponding to the NCu charge transfer. This shows that all the four

nitrogens are equivalent in these complexes.(166)

In the case of low spin square planar nickel(II) complexes, the electronic

spectra does not allow the determination of Dqxy value. The band around ca

2200023000 cm1 (which is an envelope of these transitions) has been used

successfully to correlate the NiN interactions in the case of linear tetramines(139)

and even tetrapeptides(167,168). In the case of macrocyclic complexes, the energy of

the visible absorption band is an empirical measure of the magnitude of the NiN

inplane interactions(124). A comparison of the relative positions of this band for

the nickel(II) complexes (Table 7) shows that the sequence of the NiN interaction

is not the same as the CuN interactions. However, it can be again concluded from

this comparison that 5,6,5 chelate ring sequence is the more favoured geometry for

complexation as this geometry allows a closer approach to the ideal square planar

configuration. A recent potentiometric determination of stability constants of some

nickel(II) complexes with L6, L12 and L13 and the comparison of the ‘macrocyclic

effect’ leads to similar conclusions(177).

Kinetics of acidcatalysed dissociation of the Copper(II) Complexes:

The stability of 14membered macrocyclic complexes is well recognized,

since these complexes require very high acidities(82) to force the reaction towards

dissociation (demetallation). Even at high acidities, the reactions proceed at quote

42

low rates (Table 8). The data clearly shows that in addition to the ring size, the

extent of unsaturation, Nchirality and nature of substituents also determine the

rate of dissociation. The enhanced thermodynamic stability of the metal complexes

coordinated to macrocyclic ligands as compared to the analogous non cyclic

ligands of the same denticity has been explained in terms of the macrocyclic

effect(83). The origin of this additional stability has been investigated by several

workers(122,139,169172). In kinetic terms, the macrocyclic effect can be considered as

the formation constant K = kf/kr for the equilibrium

kf M2+(solv)+Mac(solv) M (Mac)2+(solv)

kr

This effect can then be assumed to occur predominantly as a result of the

slower dissociation rate of the macrocyclic complex as compared to its linear

analogue(97) (Table 8).

The present copper(II) complexes undergo very rapid dissociation (Table 8)

in acidic solutions. A plot of kobs vs hydrogen ion concentration is shown in Fig.1

and 2. There is initially a linear dependence of kobs on [H+], but at higher hydrogen

ion concentrations the reaction becomes independent of [H+] concentrations. The

plots shows an intercept corresponding to a solvolytic path associated with these

dissociation reactions. The acid catalysed path leading to dissociation is consistent

with the following kinetic scheme(99).

K CuL2+ + H+ CuLH3+

CuLH3+ Cu2+ + HL+

The scheme involves a rapid preequilibrium protonation of the copper(II)

complex followed by a slow rate determining dissociation step. The overall rate

expression for this mechanism can be represented as

43

kobs + ko +

HKHkK

1

where ko is the solvolytic route. The above equation can be written as

kHkKkk oobs

1111

which means that a double reciprocal plot of oobs kk 1 vs H

1 should be linear

(data presented in tables 9 and 10). The present results show that this plot is linear

for both the complexes (Fig. 3 and 4). The slope of the plots gives kK1 and the

intercept gives k1 . The values of ko,k and K are presented in Table 11. A rate

constant kH (table 11) at low hydrogen ion concentration may be used for

comparative purposes, which can be defined as the slope of a plot between kobs and

[H+] at low acidities.

A general mechanism proposed for the acid catalysed dissociation of

polyamine complexes(101,173) may be adopted for these complexes as shown below:

44

The (1) (3) (4) route is the acid dependent path, while (1) (2) (4)

represents the acidindependent, solvent assisted, solvolytic dissociation path. The

protonation of the bound nitrogen in complex (1) is difficult and is reflected in the

low KMHL values of the equilibrium constant. These values are comparable to the

KMHL values reported for other complexes and lie in the range 1.8 to 10.2 M1(92,99).

At higher hydrogen ion concentrations, the decomposition of the MHL3+ species

(2) becomes rate determining and the rate constants obtained from the plots of

oobs kk 1 vs H

1 correspond to k34. This step is considerably faster than the

45

corresponding step in the unprotonated complex (k12) through the solvolytic route

(Table 11). Comparison of kH values shows that the macrocyclic complexes

undergo dissociation at a lower rate as compared to the corresponding linear amine

complexes. The breaking of the first coppernitrogen bond in steps (1) (2) and

(1) (3) involves some angular expansions of the bond angles in the chelate

rings. This results in a larger activation energy for these complexes. In the case of

normal openchain polyamine complexes, the first coppernitrogen bond breaking

involves formation of an intermediate state with the donor group displaced from

the normal position. The metal then becomes solvated and there is a rotation and

protonation of the leaving donor group. This stabilizes the intermediate species, so

that k21 or k31 is small and k21 or k13 is larger in acidic aqueous media. Thus the

breaking of the first coppernitrogen bond is rate determining in the case of

openchain amine complexes(101,173). However, in the case of the macrocyclic

complexes, the breaking of the coppernitrogen bond in steps (1) (2) or (1)

(3) is followed by the macrocyclic ligand folding or a twist instead of internal

rotation(148). The uncoordinated amine group and the metal ion are very close so

that solvation is somewhat hindered sterically. It is, therefore, possible that the

breaking of the second coppernitrogen bond is rate determining(148). The scheme

given above assumes that the dissociation at CuLH3+, involving cleavage of the

second coppernitrogen bond, is rate determining. The ligand cylisation makes

impossible the rotation of the uncoordinated amine group (of the reaction

intermediates) in the vicinity of the metal ion, resulting in a retardation of

protonation of the uncoordinated amine group and slowing down of the cleavage

of coppernitrogen bond(148).

46

The higher rates for the decomposition of these complexes as compared to

the 14membered and 18membered (L4) complexes can be accounted for on the

basis of the strain introduced by the bulky 8 and 9membered chelate rings.

The 18membered complexes(99), which carry 7,6,7,6 chelate ring sequence

have a symmetrical geometry and lesser strain in the molecules and hence

dissociate at a lower rate. The cis macrocycle [Cu(cisMe6[18]diene)N4]2+, has a

controrated conformation with a distorted tetrahedral geometry(174) around

copper(II). This complex dissociates at a comparatively very high rate. The order

of dissociation rates for the various copper(II) complexes is in the order of their

stability as reflected by the position of the visible dd absorption band(91,175). The

rate of dissociation can be directly related to the strain energy of the

macrocycle(175).

Electrochemical Studies:

Polarographic studies could be carried out on the copper(II) macrocyclic

complexes in aqueous media. The nickel(II) complexes did not show any reduction

wave, probably due to the fact that their half wave potentials are too high (above

1.6V vs S.C.E.) for the aqueous polarographic range. Cobalt(III) and

chromium(III) complexes gave highly illdefined waves and hence could not

provide any worthwhile information.

The typical polarograms of the complexes are given in Fig. 5 which show

only a single reduction wave. Plots of id vs h1/2 were found to be linear indicating

the diffusion controlled nature of the waves. Log analysis (Fig. 6) of the

polarograms showed that the complexes undergo a one electron transfer, reversible

reduction at the d.m.e. The reversible reduction of these complexes can be

assigned to the Cu2+ Cu1+ couple. A comparison of the E1/2 values (Table 12) of

47

the copper(II) complexes shows a systematic variation in their values with ring

size. The values clearly show that the reduction potential decreases with increase

in ring size. The case of reduction reflects the magnitude of the ligand field

strength and hence can be used for correlating the stability of these complexes.

The present results are in accord with those of Bhattacharya(120) and further show

that the 5,6,5 chelate sequence is the most preferred geometry for complexation.

On the basis of cyclic voltametric studies carried out in aqueous media

using NaClO4 as supporting electrolyte, Bhattacharya(120) reports a two electron

Cu2+ 2e Cu, irreversible wave for the copper(II) macrocyclic complexes with

L10, L11, L12 and L13. However the present results are at variance to this. A large

number of repetitions under various conditions showed only a single, one electron,

reversible wave for each complex studied in the present work.

48

Table 1: Analytical data for the [16] ane N4 (L7) Complexes

S.No. Compound Calc. for %C %H %N %M

Found Calc. Found Calc. Found Calc. Found Calc.

1. Ligand (L7) C12H28N4 63.0 63.15 12.0 12.28 24.40 24.56

2. L7 4HCl C12H32N4Cl4 38.38 38.50 8.40 8.55 14.80 14.97

3. [CuL7](ClO4)2 C12H28N4Cl2O8Cu 29.20 29.35 5.59 5.70 11.30 11.41 12.84 12.95

4. [NiL7](ClO4)2 C12H28N4Cl2O8Ni 29.50 29.64 5.65 5.76 11.40 11.52 11.93 12.08

5. Trans[CoL7Cl2]ClO4 C12H28N4Cl3O4Co 31.32 31.47 5.97 6.12 12.15 12.25 12.72 12.88

6. Trans[CoL7(NO2)Cl]ClO4 C12H28N6ClO8Co 29.78 30.09 5.75 5.85 17.49 17.55 12.20 12.31

7. Trans[CoL7(NO2)Cl]ClO4 C12H28N5O6Cl2Co 29.67 30.77 5.89 5.98 14.89 14.95 12.45 12.59

8. Cis[CoL7(acac)].(ClO4)2 C17H36N4Cl2O10Co 34.70 34.81 6.0 6.24 9.42 9.54 9.93 10.05

9. Cis[CoL7(glycine)].(ClO4)2 C14H32N5Cl2O10Co 29.85 30.0 5.61 5.71 12.35 12.50 10.40 10.52

10. Cis[CrL7Cl2].ClO4.H2O C12H28N4Cl3O4CrH2O 30.59 30.73 6.25 6.40 11.80 11.95 10.91 11.09

11. Cis[CrL7Cl2].Cl.H2O C12H28N4Cl3CrH2O 35.46 35.59 7.31 7.41 13.70 13.84 12.72 12.85

12. Trans[CrL7Cl2].Cl.H2O C12H28N4Cl3CrH2O 35.46 35.59 7.31 7.41 13.70 13.84 12.70 12.85

13. Trans[CrL7Cl2].ClO4.1/2H2O C12H28N4Cl3O4Cr.1/2H2O 31.20 31.33 6.20 6.31 12.03 12.18 11.15 11.31

49

Table 2: Analytical data for the [17] ane N4 (L8) Complexes

S.No. Compound Calc. for %C %H %N %M

Found Calc. Found Calc. Found Calc. Found Calc.

1. Ligand (L8) C13H30N4 64.36 64.46 12.25 12.39 23.0 23.14

2. L8 4HCl C13H34N4Cl4 40.03 40.20 8.60 8.76 14.28 14.43

3. [CuL8](ClO4)2 C13H30N4Cl2O8Cu 30.81 30.91 5.86 5.94 110.93 11.09 12.43 12.59

4. [NiL8](ClO4)2 C13H30N4Cl2O8Ni 31.12 31.20 5.91 6.0 11.06 11.20 11.64 11.78

5. Trans[CoL8Cl2]ClO4 C13H30N4Cl3O4Co 32.87 33.09 6.25 6.36 11.78 11.87 12.40 12.50

6. Trans[CoL8(NO2)Cl]ClO4 C13H30N6ClO8Co 29.42 29.54 5.59 5.68 15.80 15.91 10.9 11.10

7. Trans[CoL8(NO2)Cl]ClO4 C13H30N5O6Cl2Co 32.19 32.36 6.11 6.22 14.40 14.52 12.10 12.22

8. Cis[CoL8(acac)].(ClO4)2 C18H38N4Cl2O10Co 35.88 36.0 6.22 6.33 9.20 9.33 9.69 9.82

9. Cis[CoL8(glycine)].(ClO4)2 C15H34N5Cl2O10Co 31.21 31.36 5.78 5.92 12.0 12.19 10.12 10.26

10. Cis[CrL8Cl2].Cl.H2O C13H30N4Cl3CrH2O 37.10 37.27 7.56 7.64 13.20 13.38 12.27 12.42

11. Cis[CrL8Cl2].ClO4.1/2H2O C13H30N4Cl3O4Cr1/2H2O 32.80 32.94 6.42 6.54 11.67 11.82 10.85 10.98

50

Table 3: Electronic Spectra of [16] ane N4 (L7), [17] ane N4 (L8) and other macrocyclic complexes

S.No. Complex max (cm1) () (M1 cm1) 1. [CuL7](ClO4)2 18587(90) 37713(6064) 2. [CuL8](ClO4)2 17600 (213) 37736(6064) 3. [CuL10](ClO4)2 17600 (213) 4. [CuL2](ClO4)2 18200 (172) 5. [CuL1](ClO4)2 19900 (100) 6. [CuL14](ClO4)2 19685(92) 7. [NiL7](ClO4)2 22222sh(15) 28736sh 43103() 8. [NiL8](ClO4)2 22222sh(21) 28409() 46948()

9. [NiL14](ClO4)2 21413(64) 10. [NiL10](ClO4)2 22075(181) 11. [NiL2](ClO4)2 21600(116) 12. [NiL1](ClO4)2 22470(67) 13. Trans[CoL7Cl2]ClO4 15723(36) 20747(31)

39370sh(20922) 24510(63) 40323sh(19709)

31250(2123) 42553sh(14251)

39216(21831)

14. Trans[CoL8Cl2]ClO4 15875(13) 31746(788) 39526(8942) 15. Trans[CoL14Cl2]Cl.2H2O 16026(33) 22222sh(39) 31646(2200) 16. Trans[CoL7Cl(NO2)]ClO4 19920(77) 28090(1769)

39526(18152) 38023(18612) 40486(17450)

38610(18850) 41666(16290)

51

Table Contd… 17. Trans[CoL8Cl(NO2)]ClO4 20619(84) 28090(1509)

39526(15388) 42773sh(13908)

37736sh(15240) 40323(14796)

38462(15684) 41322(14648)

18. Trans[CoL7(NO2)2]ClO4 21459(303) 27322(4050) 39370(22170) 22735(16200)

37736(22590) 40323(20040)

38461(22810) 41494sh(18970)

19. Trans[CoL8(NO2)2]ClO4 21739(186) 27778(2649) 39526(15266) 42553(13978)

37879sh(14162) 40486(14898) 43103sh(13058)

38610(15266) 41496sh(14346)

20. Cis[CoL7(acac)](ClO4)2 19608(108) 31746(3249) 42553(19901)

21. Cis[CoL8(acac)](ClO4)2 19608(170) 26042(334) 41322(21312) 22. Cis[CoL7(glycine)](ClO4)2 20161(45) 43478(7565) 23. Cis[CoL8(glycine)](ClO4)2 20202(38) 20316sh(90) 41666(11226) 24. Trans[CoL14(NO2)2]ClO4 22624(185)

25. Cis[CoL15(acac)](ClO4)2 20080(162) 26. Cis[CoL16(glycine)](ClO4)2 20408(89) 27. Cis[CoL7(nethanolamine)cl](ClO4)2 20000

28. Trans[CrL7Cl2]ClH2O 20833(60) 24691(72) 29. Cis[CrL7Cl2]ClH2O 24509(85) 21052(54) 17543(50) 30. Cis[CrL8Cl2]ClH2O 19417(56)

52

53

Table 4: Prominent IR Absorption bands (in cm1) of [16] ane N4 (L7) Complexes

S.No. Compound (NH) (ClO4) Other ligand bands

1. Ligand (L7) 3240s

2. [CuL7](ClO4)2 3220s 1100vs, 620s

3. [NiL7](ClO4)2 3210m 1100vs, 620s

4. Trans[CoL7Cl2](ClO4) 3200s 1100vs, 620s

5. Trans[CoL7Cl(NO2)]ClO4 3200s 1100vs, 620s 1420s, 822, asym(NO2) (NO2)

6. Trans[CoL7(NO2)2]ClO4 3210s 1100vs, 620s 3150sh, 1405s, sym(NO2) asym(NO2), 822s, (NO2)

7. Cis[CoL7(acac)](ClO4)2 3230m, 3100m 1100vs, 625s 1570s, 1520s C=O and C=C of acac

8. Cis[CoL7(gly)](ClO4)2 3170m 1100vs, 625s 1340s asym(COO)

9. Cis[CrL7Cl2]ClO4H2O 3120sh, 3220s 1100vs, 620s

10. Cis[CrL7Cl2]ClH2O 3130s, 3240s

11. Trans[CrL7Cl2]ClH2O 3220s

12. Trans[CrL7Cl2]ClO41/2H2O 3230s 1100vs, 620s

shshoulder, sstrong, vsvery strong, wweak, mmedium

54

Table 5: Prominent IR Absorption bands (in cm1) of [17] ane N4 (L8) Complexes

S.No. Compound (NH) (ClO4) Other ligand bands

1. Ligand (L8) 3240s

2. [CuL8](ClO4)2 3220s 1100vs, 620s

3. [NiL8](ClO4)2 3200m 1100vs, 620s

4. Trans[CoL8Cl2](ClO4) 3200s 1100vs, 620s

5. Trans[CoL8Cl(NO2)]ClO4 3200s 1080vs, 620s 1415s, 822s asym(NO2) (NO2)

6. Trans[CoL8(NO2)2]ClO4 3180s 1080vs, 620s 1410vs, 3150vs, 822s asym(NO2), sym(NO2),

(NO2)

7. Cis[CoL8(acac)](ClO4)2 3220m, 3090m 1100vs.b,

628s

1570s, 1520s C=O and C=C of acac

8. Cis[CoL8(gly)](ClO4)2 3180m 1100vs.b,

628s

1340s asym(COO)

9. Cis[CrL8Cl2]Cl.H2O 3240sh, 3100s

10. Cis[CrL8Cl2]ClO41/2H2O 3240s, 3120s 1100vs.b, 620b

shshoulder, sstrong, vsvery strong, wweak, mmedium

55

Table 6: (dd) and enthalpy data for some copper(II) complexes with

saturated cyclic tetramines

S.No. Macrocycle (dd) cm1 H

(kJ mol1)

Chelate ring

sequence

1. L10 94.94 5,5,5,5

2. L11 18519(a) 107.11 5,6,5,5

3. L1 19900 135.56 5,6,5,6

4. L2 18200 116.32 5,6,6,5

5. L6 17600 87.50 5,5,5,7

6. L12 17094 110.88 5,6,6,6

7. L13 16529 83.60 6,6,6,6

8. L7 18587 5,6,5,8

9. L8 17600 5,6,5,9

10. L14 19685 5,6,5,6

(a) Ref. 120

Enthalpy change, H refers to the reaction;

M+2 (aq) +L (aq) ML2+ (aq)

at 25C with I = 0.5 mol mol dm3 (Ref. 35).

56

Table 7: (dd) data for some nickel(II) complexes with saturated cyclic

tetramines

S.No. Macrocycle (dd) cm1 Chelate ring sequence

1. L1 22470 5,6,5,6

2. L2 21600 5,6,6,5

3. L6 22075 5,5,5,7

4. L7 22222 5,6,5,8

5. L8 22222 5,6,5,9

6. L14 21413 5,6,5,6

Table 8: Observed first order rates for the dissociation of copper(II)

macrocyclic complexes at 25C

S.No. Complex [H+] kobs, s1 Ref.

1. [Cu(tet a)]2+ (red) 6.1 3.6107 82

2. [Cu(tet a)]2+ (unstable red) 6.1 4.3106 82

3. [Cu(tet a)]2+ (blue) 6.1 3.8103 82

4. [Cu L16]2+ 6.1 1.2103 82

5. [Cu(2,3,2tet)]2+ 6.1 4.1 82

6. [Cu L4]2+ 5.8102 2.74103 99

7. [Cu L17]2+ 1.15104 1.09102 99

8. [Cu L7]2+ 0.07 0.101 This work

9. [Cu L8]2+ 0.07 0.168 This work

57

Table 9: Kinetic data at 25C for acid catalysed dissociation of

[Cu[16]aneN4](ClO4)2

S.No. [H+] H

1 kobs/s1 ko kobsko oobs kk

1

1. 0.02 50.00 0.055 0.027 0.028 35.25

2. 0.04 25.00 0.073 0.045 22.22

3. 0.05 20.00 0.082 0.055 18.18

4. 0.06 16.67 0.091 0.064 15.63

5. 0.07 14.29 0.101 0.074 13.51

6. 0.08 12.50 0.114 0.087 11.49

7. 0.09 11.11 0.124 0.097 10.31

8. 0.10 10.00 0.135 0.108 9.26

9. 0.12 8.33 0.160 0.133 7.52

10. 0.15 6.67 0.182 0.155 6.45

11. 0.17 5.88 0.198 0.171 5.85

12. 0.20 5.00 0.218 0.191 5.25

13. 0.25 4.00 0.224 0.197 5.08

14. 0.30 3.33 0.230 0.203 4.93

15. 0.50 2.00 0.244 0.217 4.61

16. 1.00 1.00 0.250 0.223 4.48

58

Table 10: Kinetic data at 25C for acid catalysed dissociation of

[Cu[17]aneN4](ClO4)2

S.No. [H+] H

1 kobs/s1 ko kobsko oobs kk

1

1. 0.02 50.00 0.132 0.122 0.010 100.00

2. 0.03 33.00 0.142 0.020 50.00

3. 0.04 25.00 0.149 0.027 37.03

4. 0.06 16.60 0.161 0.039 25.64

5. 0.07 14.20 0.168 0.046 21.73

6. 0.08 12.50 0.172 0.050 20.00

7. 0.09 11.11 0.178 0.056 17.85

8. 0.10 10.00 0.183 0.061 16.39

9. 0.11 9.09 0.192 0.070 14.28

10. 0.15 6.66 0.204 0.082 12.19

11. 0.20 5.00 0.222 0.100 10.00

12. 0.25 4.00 0.234 0.112 8.92

13. 0.30 3.33 0.240 0.118 8.47

14. 0.50 2.00 0.250 0.128 7.81

15. 1.00 1.00 0.260 0.138 7.24

59

Table 11: Rate constants for the acidcatalyzed dissociation of macrocyclic

complexes

S.No. Complex kH [M1 S1]

ko s1 k s1 k M1 Ref.

1. [Cu(tet a)]2+ (red) 5.9108 99

2. [Cu(tet a)]2+ (unstable

red)

7.0107 99

3. [Cu(tet a)]2+ (blue) 6.2104 99

4. [Cu L18]2+ 2.0104 99

5. [Cu(2,3,2tet)]2+ 6.7101 99

6. [Cu L4]2+ 3.6102 0.80103 4.8103 10.2 99

7. [Cu L17]2+ 25 99

8. [Cu L7]2+ 1.13 0.027 0.48 2.7 This work

9. [Cu L8]2+ 0.60 0.122 0.53 1.3 This work

10. [Cu L5]2+ 2.24102 1.40103 98

Table 12: D.C. Polarographic halfwave potentials for the copper(II)

macrocyclic complexes

S.No. Copper(II) complex with

(ligand) Half wave potential E1/2

|V vs S.C.E.

In 0.1M KCl In 0.1 M NaClO4

1. L7 0.61 0.55

2. L8 0.44 0.54

3. L2 0.80 0.72

4. L19 0.50 0.47

5. L20 0.26 0.27

6. L14 0.74 0.78

60

61

62

63

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